Water and ice cause weathering in rocks by causing bits of the rock to separate and flow away through the erosion process. While this process is extremely slow, it is also inexorable, and any stone object exposed to the elements disintegrates in this way.
The Grand Canyon is one example of the effects that weathering can have over time. Over millions of years, the flow of the Colorado River etched out a giant channel in the southwestern United States that is 277 miles long, 18 miles across at its widest and a mile deep. As the water from the river breaks down the rock, small bits erode away, and no rock on Earth has the strength to keep weathering from happening.
When it comes to erosion by ice, the process happens a bit more quickly. Water seeps down into niches and crevices within rock, and it remains there until the temperature reaches the freezing point (or below). When water turns into ice, its volume expands, and the crevice increases in size. The cracking that results causes even more of the stone to erode away, and when the ice melts and the water flows out, that eroded stone goes with it.